You will need to recover your partitions, and then attempt to re-install grub using boot-repair. Hopefully the data within the partitions is still intact.
Boot an Ubuntu livecd
In terminal type
sudo parted /dev/sda
[This selects drive "sda", if you need a different drive then change appropriately.]
In Parted type
[To exit Parted type "quit".]
Install and run boot-repair.
[I won't type all that out as the Ubuntu community already has an excellent set of instructions available here: https://help.ubuntu.com/community/Boot-Repair .]
Attempting to recover deleted partitions doesn't always work, but it is always a risk. You could make things worse! If you have important data on the drive you are attempting to recover you should always perform a backup first. If you can't access the data use dd to make a sector based backup of the entire drive or partition and save it as a file.
If Parted fails to recover your partitions you can always try Gparted which also has a recovery feature. To install Gparted type "sudo apt-get install gparted" though it's often included on Ubuntu livecds.
After successfully recovering your partitions instead of running boot-repair you could re-try using your Windows installation disc's repair feature as it might now work.